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My advisor, Rowan Martindale, has been discussing climate change through geologic history in her earth history class for the last couple of weeks (including my favorite event, the Paleocene-Eocene Thermal Maximum) so in lab, we decided to have the students do an experiment to see what happens to calcium carbonate organisms in acidified water. I had recently collected some bivalve shells on a trip to the beach, so the students picked three types of shell: a mussel, which has a thin shell and acted as a control because it had both valves still attached, so one could be put in water and one in acid; a clam, which had a medium-thick shell; and an oyster, which had a very thick shell. I put the shells in glass beakers and poured in diluted hydrochloric acid, while the control valve of the mussel sat in water. The students hypothesized what would happen to each shell after one week. The class was very excited when the shells began to bubble and fizz in front of them. After a week in the fume-hood I rinsed the shells and let the students examine them. Nothing changed about the mussel in the water, however the mussel in HCl completely dissolved. In a fun twist, the periostracum, or the organic layer of the bivalve, was leftover, which looked gross but got the attention of the students. The other shells were clearly abraded, however the effect was not as dramatic as the mussel. It was a fun activity and we were able to discuss not only ocean acidification, but experimental design, hypothesis testing, as well as some of the flaws with our experiment and why the shells aren't a perfect analog for living molluscs. Below are some pictures of the experiment:
So many shells!
L,M: Carefully pouring acid into the beaker R: Our oyster fizzing in reaction to the acid
Final results after a week in acid. Control-group mussel and leftover periostracum to right side of bowl, clam and oyster to left
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